What is a dirty read?

Dirty read is a situation in a transactional database management system where one transaction reads data that has been modified by another transaction but not yet committed. If the second transaction rolls back, the first transaction has received untrustworthy data.

For example, Transaction A updates a value in a table but does not complete the transaction. Transaction B reads this updated value. If Transaction A rolls back, the data read by Transaction B will be 'dirty' and not reflect the actual state of the database.

Dirty reads violate transaction isolation and can lead to application logic errors. To prevent dirty reads, transaction isolation levels such as "Read Committed" or higher are used.